Recently, there is a demand for further thinning of a thin plate for an electronic device such as a semiconductor wafer, etc. Thus, each thin plate gets extremely thin and is easy to break regardless of its dimension.
Also, even in a case where the plate thickness does not change, enlargement of the external diameter leads to a thin-plate trend relatively from the viewpoint of the ratio between the plate thickness and the external diameter.
As a container for housing, storing, and loading such an extremely thin plate, a multistage type housing cassette described in Reference Document 1 is known. This multistage type housing cassette is a housing cassette that can load an extremely thin wafer having a thickness of 20 to 100 micrometers without causing chipping on its circumferential surface and without causing a suction error to a pad. Specifically, as shown in FIG. 20, it is a multistage type housing cassette 6 arranging vertically in parallel via braces 5 to be spaced equally a plurality of housing shelves 2 in each of which a semicircular guide 4 having a slightly larger diameter than the diameter of an extremely thin wafer w stands from a flat plate 3. A suction pad of a carrier robot is moved over the upper surface of the wafer w and is then lowered and thrusts the wafer on the flat plate to eliminate warpage of the wafer, and thereafter the wafer is attracted by suction and constrained to the suction pad.    Patent Document 1: Japanese patent publication No. 2004-273867